Paper products and methods for applying chemical additives to fibers in the manufacture of paper

ABSTRACT

In the manufacture of tissue products from cellulose fibers, it is often desirable to enhance physical properties by the addition of chemical additives, including for example debonding agents. These additives serve to prevent or disrupt interfiber or intrafiber hydrogen bonding. Depending upon the nature of the chemical additive, debonding agents may also act as softening agents. During the papermaking process, chemical additives of this type can be added to fiber slurries in the wet end of a papermaking machine. Alternately, such additives may be sprayed upon tissue layers during manufacture, prior to assembly into multi-ply tissue structures. The chemical additives may include quaternary ammonium salts or organofunctional polysiloxanes. The chemical additives may include quaternary ammonium salts or organofunctional polysiloxanes or polysiloxanes. Some of the quaternary salts which may be used include salts comprised in part of imidazoline heterocyclic nitrogen ring structures.

RELATED APPLICATIONS

[0001] The present application is a continuation-in-part application ofU.S. Ser. No. 09/589,450 filed on Jun. 7, 2000.

BACKGROUND OF THE INVENTION

[0002] In the manufacture of paper products from cellulose fibers, suchas facial tissue, bath tissue, paper towels, dinner napkins and thelike, it is often desirable to enhance product properties by theaddition of chemical additives. Properties that may be enhanced usingadditives include: dry strength, wet strength, softness, absorbency,opacity, brightness and color.

[0003] Additives provided during papermaking, such as debonding agents,may provide a softening effect by reducing inter-fiber bonding withinthe tissue structure. However, using such additives often undesirablyincreases the amount of lint or sloughing of particles from the surfaceof the tissue during use by a consumer. Also, many additives ordebonding agents undesirably reduce the strength of tissues.

[0004] Softness is a key attribute in tissue products. A feeling ofsoftness imparts to human skin a clean and soothing effect. Improvingthe balance of tissue softness and strength is a continuous effort intissue making. Tissue product designers attempt to maximize the strengthand softness of tissues. It has been recognized as a general rule oftissue manufacture that the greater the strength of a given tissue, thelower the softness of that tissue. There is usually an inverserelationship between strength and softness. In general, prior effortshave been directed at achieving softness using chemicals directed atreducing the inter-fiber bonding within the tissue structure or coatingthe tissue surface with such chemicals. Mechanical means have been usedin the art of tissue making to increase the softness of tissue paper.Many tissues are creped with a doctor blade to increase softness.Uncreped tissues sometimes are subjected to a rush transfer step toincrease softness.

[0005] During the papermaking process, additives are commonly added tofiber slurries in the wet end of a papermaking machine. Wet end chemicaladdition may provide a relatively uniform distribution of chemicaladditives on the fiber surfaces of a tissue product. Additionally, wetend chemical addition sometimes facilitates the selection of aparticular fraction to be treated with a specific chemical additive inorder to enhance the performance of the paper, or to enhance theperformance of a chemical additive. Wet end chemical addition enablesmultiple additives of various types to be added to a fiber slurry,either simultaneously or sequentially, prior to formation of the paperweb. Topical spraying, printing or size press are other methods forchemical addition.

[0006] Compositions comprising about 80% imidazoline quaternary ammoniumcompound and about 10% polyethylene glycol have been used as debondersin tissue manufacture. Witco C-6027 produced by the Witco ChemicalCompany is one product that has been used in tissue manufacture toimprove the softness of tissue. PCT International Publication WO99/34057 discloses using Witco C-6092 as a softener/debonder in tissuemanufacture.

[0007] Two component chemical softening compositions also have been usedto soften tissue. In one process, chemical debonders which includemixtures of (1) quaternary ammonium compounds, and (2) polysiloxane,have been used in the manufacture of tissue. U.S. Pat. No. 5,573,637shows the use of such a two-component quaternary/polysiloxane system intissue manufacture. Binder materials also are described as being used inconnection with such processes. A first step includes forming apapermaking aqueous furnish of fibers, including a mixture of at leastone quaternary ammonium compound, with binder materials and a wettingagent. Then, in a second step, a solution comprising a polysiloxanecompound is sprayed on the dry tissue web after creping. This two-stepprocedure, which uses quaternary compounds and a polysiloxane, has beenreported to improve tissue characteristics.

[0008] What is needed in the industry is a chemical softeningcomposition and technique of manufacture that will result in a softer,stronger tissue. A system that will provide to a final tissue product adesirable strength, with good tactile sensory softness characteristicsin a process of manufacture that is relatively simple to apply at areasonable cost would be highly desirable.

SUMMARY OF THE INVENTION

[0009] Tissues may be manufactured which exhibit softness and strengthimprovement using additives that can be applied into the wet end of apapermaking machine, or topically sprayed on the tissue web duringmanufacture. In one aspect of the invention, a tissue product is shownwhich comprises cellulosic fibers and an adsorbable chemical debondingadditive. The additive includes, in some embodiments, a quaternaryammonium salt and a surfactant. The tissue product may employ anadditive comprised of between about 10% and about 60% imidazolinequaternary ammonium salt. The tissue product also may be used in whichthe additive is comprised of or contains a lubricant.

[0010] In one alternative embodiment, the tissue product employs anadditive comprising about 19-24% low to medium charge densityimidazoline quaternary ammonium salts, about 15-20% high charge densitydialkyl imidazoline quaternary ammonium salts, about 12-19% surfacefiber lubricant, about 47-52% nonionic surfactants and wetting agents,and about 2% emulsion particle size control additives.

[0011] A multilayered product may be used, and the tissue may comprise acenter layer consisting essentially of softwood fibers and two outerlayers comprising about 50% or greater hardwood fibers. The product maybe a layered tissue.

[0012] In one aspect of the invention, at least one outer layer of thetissue is capable of absorbing an additive which is applied to thetissue by spraying following assembly of the layers of the tissue. Inone embodiment, the quaternary ammonium salt comprises in part anitrogen ring compound. In other aspects of the invention, thequaternary ammonium salt comprises in part a dinitrogen ring compound.The quaternary ammonium salt may comprise a heterocyclic compound havingmore than one type of atom in a ring structure, which may or may not bearomatic.

[0013] A method of making a tissue product is also disclosed. The methodmay include: providing a fiber furnish comprising water, cellulosicfibers, and an adsorbable chemical additive, wherein the chemicaladditive comprises an imidazoline quaternary ammonium salt and asurfactant. Then, in a next step, the fiber furnish is dewatered. Next,the fiber furnish is dried.

[0014] In another aspect of the invention, a method of making a tissueproduct is shown as follows:

[0015] (a) providing a fiber furnish of water and cellulosic fibers,

[0016] (b) dewatering the fiber furnish to form a first tissue layer,and(c) spraying upon the surface of a first tissue layer an adsorbablechemical additive, the chemical additive comprising a quaternaryammonium salt and a surfactant. It is possible to apply an additive toone or more outer layers, and then assemble the layers with one or moreother layers in a multi-layer structure. That is, one may combine thefirst tissue layer with additional tissue layers to form a layeredtissue product.

[0017] A tissue product also is presented in which the product includescellulosic fibers and an adsorbable aminofunctional polysiloxane whichis provided as a debonding agent. A method of making a tissue productalso is shown, which includes providing a fiber furnish comprisingwater, cellulosic fibers, and an adsorbable chemical additive, thechemical additive comprising an aminofunctional silicone; dewatering thefiber furnish, and then drying the fiber furnish. In some applications,hydraulic spraying of a silicone softener may be utilized. In someapplications, the silicone may be applied by spraying.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A full and enabling disclosure of this invention, including thebest mode shown to one of ordinary skill in the art, is set forth inthis specification.

[0019]FIG. 1 shows in graphical form sample data prepared as providedbelow in the Examples.

[0020]FIG. 2 is a plan view of one embodiment of a system and processfor producing uncreped through-air dried paper webs.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Reference now will be made to the embodiments of the invention,one or more examples of which are set forth below. Each example isprovided by way of explanation of the invention, not as a limitation ofthe invention. In fact, it will be apparent to those skilled in the artthat various modifications and variations can be made in this inventionwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as part of one embodimentcan be used on another embodiment to yield a still further embodiment.Thus, it is intended that the present invention cover such modificationsand variations as come within the scope of the appended claims and theirequivalents. Other objects, features and aspects of the presentinvention are disclosed in or are obvious from the following detaileddescription. It is to be understood by one of ordinary skill in the artthat the present discussion is a description of exemplary embodimentsonly, and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions.

[0022] A “debonding agent” or “debonder” refers to any chemical that canbe incorporated into paper products, such as tissue, to prevent ordisrupt interfiber or intrafiber hydrogen bonding. In general, adebonder stops the hydrogen bonding and reduces the strength of thetissue by breaking down bonds. As a general rule, use of a debondersoftens the tissue. However, a debonding agent also can cause the tissueto lint or slough, which is undesirable. Therefore, softness is normallyinversely proportional to strength when it comes to tissue.

[0023] Depending upon the nature of the chemical, debonding agents mayalso act as softening agents. A softening agent is generally anychemical additive that can be incorporated into paper products, such astissue, to provide improved tactile feel. These chemicals can also actas debonding agents or can act solely to improve the surfacecharacteristics of tissue, such as by reducing the coefficient offriction between the tissue surface and the skin on the hand.

[0024] In contrast, the term “bonding agent” refers to any chemical thatcan be incorporated into tissue to increase or enhance the level ofinterfiber or intrafiber bonding in the sheet. The increased bonding canbe either ionic, hydrogen or covalent in nature.

[0025] The current invention is geared towards the addition of adebonder or softening agent during the manufacture of a paper product,such as a tissue. Typically, the debonder is added to the tissue at anadd-on rate of from about 0.01 to about 10 weight percent of the fiber.For instance, the add-on rate may be from about 0.4 to about 7 weightpercent of the fiber.

[0026] According to the present invention, various debonders can beused. For instance, the debonder can be a blend of imidazolinequaternary ammonium salts, one or more non-ionic silicones, or one ormore aminofunctional siloxanes. The above debonders can be used alone orin combination. Further, the debonders can be added during the formationof the paper web by being combined with an aqueous slurry of fibers usedto form the web or can be applied topically to the web after the fibershave been applied to a forming fabric. Whether or not the debonder isadded at the wet end of the papermaking process or after the web hasbeen formed on the forming fabric depends upon various circumstancesincluding the debonders chosen.

[0027] In one embodiment of this invention, an additive comprising10-60% imidazoline quaternary ammonium salts, about 7-25% surface fiberlubricant, about 20%-70% nonionic surfactants and wetting agents, andabout 1-5% emulsion particle size control additives is used as thedebonder. For instance, this debonder composition can comprise betweenabout 40% and 60% quaternary ammonium salts by weight, and in stillanother embodiment the composition comprises about 50% quaternaryammonium salts by weight.

[0028] The quaternary ammonium salt may comprise in part a nitrogen ringcompound. For instance, the quaternary ammonium salt may comprise adinitrogen ring compound. The salt may comprise a heterocyclic compoundhaving more than one type of atom in a ring structure, which may or maynot be aromatic.

[0029] In one embodiment, the composition may be comprised of a blend ofquaternary ammonium salts with differing charge densities. For instance,the composition can comprise about 15-30% of a low to medium chargedensity imidazoline quaternary ammonium salt and about 10-25% of a highcharge density dialkyl imidazoline quaternary ammonium salts, about7-25% surface fiber lubricant, about 20-70% nonionic surfactants andwetting agents, and about 1-5% emulsion particle size control additives.

[0030] For instance, in one embodiment of the current invention, QuaSoft229 may be used as the debonder. QuaSoft 229 is a composition that ismanufactured and distributed by the Quaker Chemical Corporation ofConshohocken, Pennsylvania (“QuaSoft 229” is believed to be a trademarkof the Quaker Chemical Company).

[0031] QuaSoft 229 is believed to comprise about 19-24% low to mediumcharge density imidazoline quaternary ammonium salts, about 15-20% highcharge density dialkyl imidazoline quaternary ammonium salts, about12-19% surface fiber lubricant, about 47-52% nonionic surfactants andwetting agents, and about 2% emulsion particle size control additives.The nonionic surfactants in the QuaSoft 229 are polyethylene glycol andpolypropylene glycol esters and the lubricant is a lanoline derivative.

[0032] The low to medium charge density imidazoline quaternary ammoniumsalts described above have a charge density of less than about 0.7meq/g. For instance, in one embodiment the charge density is less thanabout 0.5 meq/g, such as from about 0.25 meq/g to about 0.42 meq/g whenpresent in a neat or concentrated form. The molecular weight of the lowto medium charge density imidazoline quaternary ammonium salts, in oneembodiment, can be from about 1250 to about 1300.

[0033] The high charge density imidazoline quaternary ammonium salts canhave a charge density greater than about 0.9 meq/g. For instance, in oneembodiment, the charge density can be greater than about 1.2 meq/g, suchas from about 1.22 meq/g to about 1.23 meq/g when present in the neatform. In one embodiment, the high charge density imidazoline quaternaryammonium salts can have a molecular weight of from about 650 to about700.

[0034] As described above, the above charged density ranges are for thecomponents in a neat form. When contained in a debonder composition,however, the charge densities can be diluted. For example, if a low tomedium charge density imidazoline quaternary ammonium salt is present inthe composition in an amount of 21% by weight, the charge density of thesalt in the solution can be from about 0.07 meq/g to about 0.09 meq/g.If a high charge density imidazoline quaternary ammonium salt is presentin an amount of 17% by weight, the salt can have a charge density offrom about 0.20 meq/g to about 0.21 meq/g.

[0035] In the QuaSoft 229 product, the difference in charge densities inthe quaternary ammonium salts is believed to be due to the amount ofconverted tertiary amines present. For example, the high charge densityquaternary ammonium compounds show a high degree of conversion of thetertiary amines to the quaternary positively charged amines. Thelow/medium density quaternary amines contain more unconverted tertiaryamines. However, tertiary amines do not carry any charge, and thus theoverall charge density is less for that reason. Including in thecomposition a certain amount of tertiary amines has been observed toimprove handfeel. Therefore, in a preferred composition of theinvention, quaternary amines having both relatively high and relativelylow charge densities are provided.

[0036] QuaSoft 229 applied at the wet end of the papermaking process mayincrease surface softness while maintaining an acceptable base sheetstrength. It has been discovered by the present invention, however, thattopically applying the composition directly on the sheet will provideincreased surface softness at similar strength levels. In addition,increasing the amount of chemical softener in the sheet of tissue,either by wet end addition or topical application, improves the surfacesoftness at similar strength levels when compared to other debondingagents. This may be due to the increased amount of composition that isretained on the tissue surface.

[0037] In another embodiment of the current invention, a non-ionicsilicone emulsion may be used as the debonder. This emulsion may be usedin conjunction with an imidazoline quaternary ammonium salt compositionas described above or another debonder.

[0038] In one embodiment, one such non-ionic silicone emulsion additiveis Dow Corning DC-2-5304. This additive is a white liquid comprising (byweight) about 40-70% water; 30-60% polydimethylsiloxane (molecularweight of from 8,000 to 12,000); 5-10% dimethyl, methylhydroxypropyl,ethoxylated propoxylated siloxane; 3-7% polyethylene oxide, propyleneoxide) monoallyl ether; and 1-5% alkoxy polyethoxy ethanol.

[0039] In a further embodiment of the current invention, anaminofunctional siloxane in a cationic emulsion may be used as thedebonding agent. In one particular embodiment, DC-2-8050, a cationicemulsion manufactured by Dow Corning Corp. of Midland, Mich., may beused as the debonder. DC-2-8050 debonder includes from about 15% toabout 40% by weight of an aminofunctional siloxane (molecular weight offrom 30,000 to 40,000), from about 7% to about 13% by weight ofpolyoxyethylated tridecyl alcohol, from about 7% to about 13% by weighthexadecyltrimethyl ammonium chloride, and from about 3% to about 7% byweight octamethyl cyclotetrasiloxane.

[0040] Any of the debonders mentioned above are added during themanufacture of the tissue. The addition may be at the wet end or appliedto the surface of a formed sheet. When applied to the surface of a paperproduct, the debonder composition can be applied by spraying,rotogravure printing, trailing blade coating, flexographic printing, andthe like.

[0041] In general, the debonder composition of the present invention canbe applied to any suitable paper product, such as bath tissue, facialtissue, paper towels, industrial wipers, and the like. The paper productcan be made in any suitable manner. For instance, paper productsutilized in the present invention can be made utilizing adhesivecreping, wet creping, double creping, embossing, wet-pressing,air-pressing, through-air drying, creped through-air drying, uncrepedthrough-air drying, as well as other steps known in the paper art. Byway of illustration, various tissue making processes are disclosed inU.S. Pat. No. 5,607,551 issued Mar. 4, 1997 to Farrington and U.S. Pat.No. 5,667,636 issued Sep. 16, 1997 to Engel et al., which areincorporated herein by reference.

[0042] A variety of conventional papermaking apparatus may be used inthe application of this invention, as they are known by persons of skillin the art. Conventional operations may be used with respect to thestock preparation, headbox, forming fabrics, web transfers, and crepingand drying.

[0043] Stock preparation equipment may be used to apply chemicaladditives to papermaking fibers according to one embodiment of thepresent invention. The stock preparation equipment may include a firststock chest, a second stock chest, and a dewatering device between thestock chests. Papermaking fibers and water are added to the first stockchest to form a fiber slurry. The fiber slurry in the first stock chesttypically has a consistency of about 20% or lower, and particularlyabout 5% or lower, such as about 3 to about 5%. The fiber slurry in thefirst stock chest is desirably under agitation using a mixing blade,rotor, recirculation pump, or other suitable device for mixing the fiberslurry.

[0044] When the debonding agent is added in the wet end of thepapermaking apparatus, one or more chemical additives are supplied froma reservoir and added to the fiber slurry in the first stock chest. Theamount of chemical additive may range from about 5 to about 20kg./metric ton in the outer layer of the web. In particular embodiments,the chemical additive comprises a blend of imidazoline-based debondingagents and is added to one layer of the fiber furnish in an amount fromabout 7.5 to about 15 kg./metric ton, or more. The range provided issimply a workable range, and in no way is intended to be limiting of thescope of the invention. The fiber slurry and chemical additive aredesirably allowed to remain together in the first stock chest underagitation for a residence time sufficient to allow the papermaking fiberto absorb a substantial portion of the chemical additive. A residencetime of about 15 to about 30 minutes, for instance, may be sufficient.

[0045] The fiber slurry is thereafter transferred through suitableconduits and a pump to the dewatering device. In this illustratedembodiment, the dewatering device can comprise a belt press, althoughalternative dewatering devices such as a centrifuge, a nip thickeningdevice or the like may be used. The fiber slurry is injected between apair of foraminous fabrics such that press filtration is removed fromthe slurry. The press filtrate comprises a portion of the process wateralong with unabsorbed chemical additives in the water. The belt press orother dewatering device suitably increases the fiber consistency of theslurry to about 20% or greater, and particularly about 30% or greater.The unabsorbed chemical additive can be removed from the process or usedas dilution water in prior stock preparation steps, but importantly itis not sent forward with the chemically treated finish.

[0046] In those applications for which two stock chests are used, thethickened fiber slurry is then transported through conduits to a secondstock chest. The fiber slurry is then re-diluted with fresh water from asuitable reservoir and optionally agitated using a mixing device. Thefiber consistency of the slurry is suitably decreased to about 20% orless, and particularly about 5% or less, such as about 3 to about 5%.The fiber slurry may then be removed from the second stock chest throughsuitable conduits and a pump for subsequent processing. Alternatively,the fiber slurry may be processed through the foregoing procedure againin an effort to further increase the chemical additive retention level.

[0047] In an alternative embodiment of the present invention, the stockpreparation equipment may be used to apply chemical additives topapermaking fibers and to mechanically treat the fibers. Thus, theequipment used may optionally comprise three stock chests, twodewatering devices, two dilution water chests, and a disperser formechanically treating the papermaking fibers.

[0048] Papermaking fibers and water are added to the first stock chestto form a fiber slurry. The fiber slurry in the first stock chestdesirably has a consistency of about 20% or lower, and particularlyabout 5% or lower. One or more chemical additives are supplied from areservoir and added to the fiber slurry in the first stock chest whileunder agitation.

[0049] After a sufficient residence time, the fiber slurry istransferred through suitable conduits and a pump to a belt press orother suitable dewatering device. Unabsorbed chemical additives in thewater are removed with the press filtrate during the pressing operationand stored in the first dilution water chest. The contents of the firstdilution water chest may be used as either pulper make-up water ordilution water or may be discarded. The dewatering device suitablyincreases the fiber consistency of the slurry to about 20% or greater,and particularly about 30% or greater.

[0050] The thickened fiber slurry is then transported through suitableconduits to the disperser for mechanical treatment of the fibers.Dispersers suitable for use in the present method are disclosed in U.S.Pat. Nos. 5,348,620 and 5,501,768 which are incorporated herein byreference.

[0051] After dispersing, the fiber slurry may be transported viaconduits to a second stock chest. A second chemical additive or secondgroup of chemical additives may be supplied from a reservoir and addedto the fiber slurry in the second stock chest while under agitation.Additionally, the fiber slurry may optionally be diluted with filtratefrom a source described hereinafter. The fiber consistency of the slurrysuitably decreases to about 20% or lower, and particularly about 5% orlower, such as about 3 to about 5%. In particular embodiments, thesecond chemical additive comprises a softening agent and/or a debondingagent, and the fiber slurry is not subjected to high shear refiningforces such as those generated in a disperser once the softening and/ordebonding agent is added to the fiber slurry.

[0052] One suitable process for making paper products from the fiberslurries is the uncreped through-air drying method (UCTAD). One or moreembodiments of the uncreped through-air drying method is disclosed inU.S. Pat. 5,656,132 to Farrington, Jr. et al., which is incorporatedherein by reference.

[0053] As shown in FIG. 2, a twin wire former having layered papermakingheadbox 10 injects or deposits a stream 11 from the fiber slurry ontothe forming fabric 13 to form a cellulosic web. The web is thentransferred to fabric 17 which serves to support and carry thenewly-formed wet web downstream in the process as the web is partiallydewatered to a consistency of about 10 dry weight percent. Additionaldewatering of the wet web can be carried out, such as by vacuum suction,while the wet web is supported by the fabrics.

[0054] The transfer fabric 17 travels at a slower speed than the formingfabric in order to impart increased MD (machine direction) stretch intothe web. A so-called “kiss” transfer is completed in many embodiments toavoid compression of the wet web, preferably with the assistance of avacuum shoe. The transfer fabric may be a fabric having impressionknuckles or it may be a smoother fabric such as Asten 934, 937, 939, 959or Albany 94M, which are fabrics known to persons of skill in the art.

[0055] If the transfer fabric is of the impression knuckle typedescribed herein, it can be utilized to impart some of the sameproperties as the through-air drying fabric and can enhance the effectwhen coupled with a through-air drying fabric also having the impressionknuckles. When a transfer fabric having impression knuckles is used toachieve the desired CD (cross direction) stretch properties, it providesthe flexibility to optionally use a different through-air drying fabric,such as one that has a decorative weave pattern, to provide additionaldesirable properties not otherwise attainable.

[0056] The web then may be transferred from the transfer fabric to athrough-air drying fabric 19 with the aid of a vacuum transfer roll 20or a vacuum transfer shoe. The through-air drying fabric typicallytravels at about the same speed or a different speed relative to thetransfer fabric. If desired, the through-air drying fabric may be run ata slower speed to further enhance MD (machine direction) stretch.Transfer is preferably carried out with vacuum assistance to ensuredeformation of the sheet to conform to the through-air drying fabric,thus yielding desired bulk, flexibility, CD stretch and appearance. Thethrough-air drying fabric is preferably of the impression knuckle type,but it is not necessary that it be of that type.

[0057] The level of vacuum used for the web transfers can be from about3 to about 15 inches (about 75 to about 380 millimeters) of mercury,such as from about 10 to about 15 inches (about 254 to about 380millimeters) of mercury. The vacuum shoe (negative pressure) used in therush transfer step can be supplemented or replaced by the use ofpositive pressure from the opposite side of the web to blow the web ontothe next fabric in addition to or as a replacement for sucking it ontothe next fabric with vacuum. Also, a vacuum roll or rolls can be used toreplace the vacuum shoes.

[0058] While supported by the through-air drying fabric, the web isfinal dried to a consistency of about 94% or greater by the throughdryer21 and thereafter transferred to a carrier fabric 22. The dried base 23sheet is transported to the reel 24 using carrier fabric 22 and anoptional carrier fabric 25. An optional pressurized turning roll 26 canbe used to facilitate transfer of the web from carrier fabric 22 tofabric 25.

[0059] Many fiber types may be used in the practice of the presentinvention including hardwood or softwoods, straw, flax, milkweed seedfloss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like.Numerous different types of papermaking fibers may be employed,including bleached and unbleached fibers, fibers of natural origin(including wood fiber and other cellulosic fibers, cellulosederivatives, and chemically stiffened or crosslinked fibers), somecomponent portion of synthetic fibers (synthetic papermaking fibersinclude certain forms of fibers made from polypropylene, acrylic,aramids, acetates, and the like), virgin and recovered or recycledfibers, hardwood and softwood, and fibers that have been mechanicallypulped (e.g., groundwood), chemically pulped (including but not limitedto the kraft and sulfite pulping processes), thermomechanically pulped,chemithermomechanically pulped, and the like.

[0060] Mixtures of any subset of the above mentioned or related fiberclasses may be used. The fibers can be prepared in a multiplicity ofways known to be advantageous in the art. Useful methods of preparingfibers include dispersion to impart curl and improved drying properties.

[0061] Further, a single headbox or a plurality of headboxes may be usedin the practice of the invention. The headbox or headboxes may bestratified to permit production of a multilayered structure from asingle headbox jet in the formation of a web. In particular embodiments,the web may be produced with a stratified or layered headbox topreferentially deposit shorter fibers on one side of the web forimproved softness, with relatively longer fibers on the other side ofthe web or in an interior layer of a web having three or more layers.The web is desirably formed on an endless loop of foraminous formingfabric which permits drainage of the liquid and partial dewatering ofthe web. Multiple embryonic webs from multiple headboxes may be couchedor mechanically or chemically joined.

[0062] In one embodiment, the formed paper web contains three layers offibers. In particular, the web may contain a middle layer of softwoodfibers surrounded by two outer layers of hardwood fibers. Paper brokecan also be added to the outer layers in an amount less than about 25%by weight of the layer, for instance, in an amount of less than about10% by weight of the layer. In this embodiment, each of the outer layerscan comprise from about 20% to about 40% of the total weight of the web.

[0063] The debonder may also be applied using topical application, suchas spraying, as opposed to addition at the wet end. In fact, the presentinvention has discovered that, in some embodiments, certain debondersmay yield better results from topical application than wet end addition.Spraying is performed using a spray nozzle which adds the debonder tothe tissue. In one embodiment, the debonder may be applied to the toplayer of the tissue, or upon the layer that will ultimately become thetop layer of the tissue. The debonder may also be applied to the outerlayers of a multi-layer tissue. The debonder may require dilution withwater when applying using a spraying method. For example, the debondermay be present in an aqueous composition in an amount less than about30% by weight, such as in an amount less than about 20% by weight. Forexample, in one embodiment, the debonder can be present in an aqueouscomposition in an amount less than about 10% by weight, such as lessthan 5% by weight. In one particular embodiment, the debonder can bepresent in an aqueous composition in an amount less than about 3% byweight.

[0064] In applying a debonder topically, the amount of moisturecontained in the debonder composition and contained within the web canbe adjusted to optimize results. For instance, in a three layer tissuecontaining a softwood layer surrounded on each side by a hardwood layer,the softwood layer serves as the strength layer. In this embodiment, thedebonder can be added topically such that it does not substantiallymigrate to the softwood layer. In particular, the less moisture added tothe outer layers or present in the outer layers, the less chance thereis of migration to the inner softwood layer. Further, the lessmigration, the more debonder remains on the outer layers that actuallycontact the user.

[0065] The amount of moisture contained within the web when the debondercomposition is applied to the web can vary depending on the particularapplication and process conditions. In general, the consistency of theweb can be from about 20% to about 80%. More particularly, theconsistency of the web can be from about 25% to about 60%.

[0066] In one embodiment, application of the debonder is performedbetween a rush transfer step and a through-air drying step. Prior to thethrough air drying step, the consistency of the web in one embodiment isless than about 40% such as from about 25% to about 29%. For instance,in one embodiment, the consistency is from about 26% to about 29% afterrush transfer and prior to drying.

[0067] In an alternative embodiment, the papermaking process can includea first through-air dryer and a second consecutive through-air dryer.Application of the debonder can be performed in between the through-airdryers. In this embodiment, the consistency of the web can be from about40% to about 80%.

[0068] Other chemical additives may be used in conjunction with thepresent invention. These additives include: dry strength aids, wetstrength aids, softening agents, debonding agents, absorbency aids,sizing agents, dyes, optical brighteners, chemical tracers, opacifiers,dryer adhesive chemicals, and the like. Additional forms of chemicaladditives may include: pigments, emollients, humectants, virucides,bactericides, buffers, waxes, fluoropolymers, odor control materials anddeodorants, zeolites, perfumes, debonders vegetable and mineral oils,humectants, sizing agents, superabsorbants, surfactants, moisturizers,UV blockers, antibiotic agents, lotions, fungicides, preservatives,aloe-vera extract, vitamin E, or the like. Suitable chemical additivesare adsorbable by the cellulosic papermaking fiber and are usually watersoluble or water dispersible.

[0069] The following Examples serve to illustrate possible approachespertaining to the present invention. The particular amounts,proportions, compositions, and parameters are meant to be exemplary, andare not intended to specifically limit the scope of the invention.

EXAMPLES 1-3

[0070] An uncreped through air dried tissue product was used in thisExample. The chemicals screened included the three following examples:

[0071] 1) QuaSoft 229 (i.e. codes QS-2, QS-3, QSWE-2) (applied at eitherthe wet end or by spraying)

[0072] 2) aminofunctional siloxane, DC-2-8050, a cationic emulsionmanufactured by Dow Corning of Midland, Mich. (codes AFS-2 and AFS-3)(applied at the wet end)

[0073] 3) nonionic silicone emulsion, DC-2-5304, manufactured by DowCorning of Midland, Mich. (codes SC-2 and SC-3) (applied by hydraulicspraying after rush transfer and before through air drying).

[0074] The speed of the continuous sheet former machine used in thetesting was about 50 ft./minute.

[0075]FIG. 1 shows a graph of softness (designated as IHR) versusProduct Strength. Product strength refers to tissue strength, asmeasured in GMT (geometric mean tensile strength). Positive IHR scoresindicate that more of the attribute is present, while negative scoresindicate that less of the attribute is present. For purposes of thistesting, the designations on FIG. 1 are as follows:

[0076] AFS=aminofunctional silicone;

[0077] QS=QuaSoft 229;

[0078] QSWE=QuaSoft 229 applied at the wet end of the papermakingprocess;

[0079] C6027=Witco's C-6027 product;

[0080] SC=nonionic silicone composition

[0081] Numerals following a letter designation indicate different runnumbers.

[0082] Samples containing a non-ionic silicone, an aminofunctionalsilicone and QuaSoft 229 showed surprisingly good results in this test,especially as compared to the control (C-6027). FIG. 1 illustrates theproduct results for the control (C-6027) and seven test variants(hereafter called “codes”). The chemicals applied by spraying arerepresented by codes QS2, QS3, SC2, SC3, the others were added at thewet-end (AFS2, AFS3, QSWE2 and C-6027).

[0083] All codes were showed greater softness characteristics than thecontrol (C-6027; Witco product) even though the control had the lowestGMT. These results represent a surprising and unexpected departure fromthe regular softness/strength curve. That is, although one usually seesan inverse correlation between strength and softness, no such inversecorrelation is seen in the codes as compared to the control in theseresults.

[0084] Of particular interest, the results in FIG. 1 show that when thedebonder composition containing the blend of the imidazoline quaternaryammonium salts is applied to the paper product, an increase in softnessoccurs when the composition is applied topically as opposed to beingapplied at the wet end.

[0085] Samples are shown below in Table 1. TABLE 1 Codes for SamplesUsed in Testing Type of Target add-on rate Code Softener Application ontotal basesheet Control C-6027 Wet-end 0.48% actives AFS-2 2-8050Wet-end 0.48% actives AFS-3 2-8050 Wet-end 1.3% actives SC-2 2-5304Hydraulic spray 0.75% actives SC-3 2-5304 Hydraulic spray 1.75% activesQS-2 QuaSoft 229 Hydraulic spray 2.92% total solids QS-3 QuaSoft 229Hydraulic spray 5.1% total solids QSWE-2 QuaSoft 229 Wet-end 5.1% totalsolids

[0086] The spraying equipment used comprised Quick Veejet Spray Nozzles:#650017 capacity/size with a 40 psi/0.017 gal/min nozzle. The modelmachine was set up to simulate the uncreped through-air drying processfor the trial. Headbox #1 was used to form the outer layer of the sheetwith Headbox #2 adding the middle layer of sheet.

[0087] The spray boom was located on the #3 fabric run between rolls,just after the vacuum slot on the fabric. The spray fans were aimeddirectly at the sheet. Given the configuration of the machine, thisresulted in the chemistry being sprayed at the outer layer (which wasalso the layer supported by the fabric). This is consistent for topicalapplication for a normal three strata tissue structure, since the outerstrata are comprised predominantly of eucalyptus fiber.

[0088] Two nozzles were placed to improve uniformity. A plastic tent andevacuation system was arranged. The concentration of the chemicalsolutions was adjusted accordingly to obtain the desired target add-on.Water, tinted with food coloring was used to visually set the spraydistance at approximately 12 inches. For this trial, the geometry andpressure were maintained constant.

[0089] In the tests using a wet end application, a Parez 631-NC productmanufactured by Cytec is a glyoxylated polyacrylamide temporary wetstrength resin. The glyoxylated polyacrylamide wet strength resin wasadded to the machine chest and mixed for 15-20 min. Softener was addedafterwards to the machine chest and mixed for about 20 min. Sheetstrength target was set at 750 @50 GMT.

[0090] It is understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions. The invention is shown by example in the appended claims.

What is claimed:
 1. A tissue product, comprising: (a) cellulosic fibers,and (b) an adsorbable chemical debonding additive, wherein the additivecomprises at least two quaternary ammonium salts, the quaternaryammonium salts comprising a first imidazoline quaternary ammonium salthaving a first charge density and a second imidazoline ammonium salthaving a second charge density, the first charge density being greaterthan about 0.9 meq/g and the second charge density being less than about0.7 meq/g when the ammonium salts are in a neat form, and wherein thequaternary ammonium salts comprise between about 10% and 60% by weightof the additive when water is not present.
 2. The tissue product ofclaim 1, wherein the quaternary ammonium salts comprise between about40% and about 60% by weight of the additive when water is not present.3. The tissue product of claim 1, in which the debonding additivecomprises by weight, (i) about 19-24% of the first imidazolinequaternary ammonium salt; and (ii) about 15-20% of the secondimidazoline quaternary ammonium salt.
 4. The tissue product of claim 1,in which the additive further comprises of between about 12-19%lubricant by weight.
 5. The tissue product of claim 1, in which theadditive further comprises about 20-70% by weight nonionic surfactants.6. The tissue product of claim 1, in which the additive comprisesbetween about 34% and about 44% by weight of the imidazoline quaternaryammonium salts.
 7. The tissue product of claim 1, in which the tissueproduct is multi-layered.
 8. The tissue product of claim 7, in which thetissue product includes a middle layer positioned in between a firstouter layer and a second outer layer of fibers, the first and secondouter layers comprising hardwood fibers, the middle layer comprisingsoftwood fibers.
 9. The tissue product of claim 8, in which thedebonding additive is applied to the tissue product such that theadditive is substantially only present in the first and second outerlayers.
 10. The tissue product of claim 1, wherein the debondingadditive has been applied to at least one surface of the tissue product.11. The tissue product of claim 10, in which the debonding additive hasbeen applied to both sides of the tissue product.
 12. The tissue productof claim 1, wherein the first charge density is from about 1.22 meq/g toabout 1.23 meq/g.
 13. The tissue product of claim 1, wherein the secondcharge density is from about 0.35 meq/g to about 0.42 meq/g.
 14. Amethod of making a tissue product, comprising: (a) providing a fiberfurnish of water and cellulosic fibers, (b) forming the fiber furnishinto a tissue layer, and (c) applying to the surface of the tissue layeran adsorbable chemical additive, the chemical additive comprising amixture of quaternary ammonium salts, the mixture comprising a firstimidazoline quaternary ammonium salt, and a second imidazolinequaternary ammonium salt.
 15. The method of claim 14 further comprisingthe step of: (d) combining the tissue layer with additional tissuelayers to form a layered tissue product.
 16. The method of claim 14further comprising the steps of: (d) providing a second fiber furnish toform a second tissue layer, (e) spraying upon the surface of the secondtissue layer the adsorbable chemical additive, and (f) forming thetissue product using the tissue layers as outer plies.
 17. The method ofclaim 14, wherein the first imidazoline quaternary ammonium salt has afirst charge density and the second imidazoline quaternary ammonium salthas a second charge density, the first charge density being greater thanabout 0.9 meq/g, the second charge density being less than about 0.7meq/g.
 18. The method of claim 17, wherein the first charge density isfrom about 1.22 meq/g to about 1.23 meq/g.
 19. The method of claim 17,wherein the second charge density is from about 0.35 meq/g to about 0.42meq/g.
 20. The method of claim 14, wherein the additive is applied tothe tissue layer when the tissue layer has a consistency of greater thanabout 20%.
 21. The method of claim 14, wherein the additive is appliedto the tissue layer when the tissue layer has a consistency of greaterthan about 25% and less than about 80%.
 22. The method of claim 14,wherein the additive is applied to the tissue layer in between a rushtransfer operation and a through-air drying operation.
 23. The method ofclaim 14, wherein the additive is applied to the tissue layer in betweena first through-air drying operation and a second through-air dryingoperation.
 24. The method of claim 14, wherein the tissue layercomprises a stratified fiber furnish including a first layer and asecond layer, the first layer comprising hardwood fibers, the secondlayer comprising softwood fibers.
 25. The method of claim 24, whereinthe additive is applied to the first layer containing hardwood fibers,the additive being applied in a manner such that substantially all ofthe additive is contained within the first layer containing the hardwoodfibers.
 26. The method of claim 14, wherein the tissue layer comprises astratified fiber furnish including a middle layer positioned between afirst outer layer and a second outer layer, the first and second outerlayers comprising hardwood fibers, the middle layer comprising softwoodfibers.
 27. The method of claim 26, wherein the additive is applied tothe first outer layer and the second outer layer, the additive beingapplied in a manner such that the additive remains substantially withinthe first and second outer layers without migrating to the middle layer.28. The method of claim 14, wherein the additive further comprises alubricant and a surfactant.
 29. The method of claim 28, wherein thelubricant comprises a lanolin derivative.
 30. The method of claim 28,wherein the surfactant comprises a polyethylene glycol ester, apolypropylene glycol ester, or mixtures thereof.
 31. A tissue productcomprising: a paper web comprising cellulosic fibers; and an adsorbablechemical debonding additive topically applied to the paper web, thedebonding additive being present in the web in an amount of from about0.01% to about 10% by weight, the debonding additive comprising anaminofunctional siloxane or a nonionic siloxane, the debonding additivebeing applied to the paper web while the web has a consistency of lessthan about 80%.
 32. A tissue product as defined in claim 31, wherein thenon-ionic silicone comprises polydimethylsiloxane.
 33. A tissue productas defined in claim 31, wherein the debonding additive is applied to thepaper web when the paper web is at a consistency of less than about 60%.34. A tissue product as defined in claim 31, wherein the debondingadditive is applied to the paper web when the paper web is at aconsistency of less than about 40%.